GMOS IFU observations of the stellar and gaseous kinematics in the centre of NGC 1068

We present a data cube covering the central 10 arcsec of the archetypal active galaxy NGC 1068 over a wavelength range 4200–5400 Å obtained during the commissioning of the integral field unit (IFU) of the Gemini Multi-object Spectrograph (GMOS) installed on the Gemini-North telescope. The data cube shows a complex emission line morphology in the [O iii] doublet and Hβ line. To describe this structure phenomenologically we construct an atlas of velocity components derived from multiple Gaussian component fits to the emission lines. The atlas contains many features which cannot be readily associated with distinct physical structures. While some components are likely to be associated with the expected biconical outflow, others are suggestive of high velocity flows or disc-like structures. As a first step towards interpretation, we seek to identify the stellar disc using kinematical maps derived from the Mg b absorption line feature at 5170 Å and make associations between this and gaseous components in the atlas of emission line components

Measurement of throughput variation across a large format volume-phase holographic grating

In this paper, we report measurements of diffraction efficiency and angular dispersion for a large format (~ 25 cm diameter) Volume-Phase Holographic (VPH) grating optimized for near-infrared wavelengths (0.9 ~ 1.8 μm). The aim of this experiment is to see whether optical characteristics vary significantly across the grating. We sampled three positions in the grating aperture with a separation of 5 cm between each. A 2 cm diameter beam is used to illuminate the grating. At each position, throughput and diffraction angle were measured at several wavelengths. It is found that whilst the relationship between diffraction angle and wavelength is nearly he same at the three positions, the throughputs vary by up to ~ 10% from position to position. We explore the origin of the throughput variation by comparing the data with predictions from coupled-wave analysis. We find that it can be explained by a combination of small variations over the grating aperture in gelatin depth and/or refractive index modulation amplitude, and amount of energy loss by internal absorption and/or surface reflection

A systematic cross-search for radio/infrared counterparts of XMM-Newton sources

We present a catalog of cross-correlated radio, infrared and X-ray sources using a very restrictive selection criteria with an IDL-based code developed by us. The significance of the observed coincidences was evaluated through Monte Carlo simulations of synthetic sources following a well-tested protocol. We found 3320 coincident radio/X-ray sources with a high statistical significance characterized by the sum of error-weighted coordinate differences. For 997 of them, 2MASS counterparts were found. The percentage of chance coincidences is less than 1%. X-ray hardness ratios of well-known populations of objects were used to provide a crude representation of their X-ray spectrum and to make a preliminary diagnosis of the possible nature of unidentified X-ray sources. The results support the fact that the X-ray sky is largely dominated by Active Galactic Nuclei at high galactic latitudes (|b| >= 10^\circ). At low galactic latitudes (|b| <= 10^\circ) most of unidentified X-ray sources (~94%) lie at |b| <= 2^\circ. This result suggests that most of the unidentified sources found toward the Milky Way plane are galactic objects. Well-known and unidentified sources were classified in different tables with their corresponding radio/infrared and X-ray properties. These tables are intended as a useful tool for researchers interested in particular identifications.Comment: Accepted for publication in Ap&SS. 47 pages, 10 figures. On-line material: figures and table

Applications of Integrated Photonic Spectrographs in astronomy

One of the problems of producing instruments for extremely large telescopes (ELTs) is that their size (and hence cost) scales rapidly with telescope aperture. To try to break this relation alternative new technologies have been proposed, such as the use of the Integrated Photonic Spectrograph (IPS). Due to their diffraction-limited nature, the IPS is claimed to defeat the harsh scaling law applying to conventional instruments. In contrast to photonic applications, devices for astronomy are not usually used at the diffraction limit. Therefore, to retain throughput and spatial information, the IPS requires a photonic lantern (PL) to decompose the input multi-mode light into single modes. This is then fed into either numerous arrayed waveguide gratings (AWGs) or a conventional spectrograph. We investigate the potential advantage of using an IPS instead of conventional monolithic optics for a variety of capabilities represented by existing instruments on 8 m telescopes and others planned for ELTs. To do this, we have constructed toy models of different versions of the IPS and calculated the relative instrument sizes and the number of detector pixels required. This allows us to quantify the relative size/cost advantage for instruments aimed at different science requirements. We show that a full IPS instrument is equivalent to an image slicer. Image slicing is a beneficial strategy for ELTs as previously demonstrated. However, the requirement to decompose the input light into individual modes imposes a redundancy in terms of the numbers of components and detector pixels in many cases which acts to cancel out the advantage of the small size of the photonic components. However, there are specific applications where an IPS gives a potential advantage which we describe. Furthermore, the IPS approach has the potential advantage of minimizing or eliminating bulk optics. We show that AWGs fed with multiple single-mode inputs from an PL require relatively bulky auxiliary optics and a 2D detector array which significantly increases the size of the instrument. A more attractive option is to combine the outputs of many AWGs so that a 1D detector can be used to greatly reduce the number of detector pixels required and provide efficient adaptation to the curved output focal surface

Coupling starlight into single-mode photonic crystal fiber using a field lens

We determine the coupling characteristics of a large mode area (LMA) photonic crystal, single-mode fiber when fed with an on-axis field lens used to place an image of the telescope exit pupil at the fiber input. The maximum field of view is found to be approximately the same as that of feeding the fiber directly with the telescope PSF in the image plane. However, the field lens feed can be used to provide a flat, maximised coupling response over the entire visible-NIR which is not possible using either the highly wavelength dependent direct feed coupling to the LMA fiber or the attenuation spectrum limited step index fiber cases

Strategies for spectroscopy on Extremely Large Telescopes - II. Diverse-field spectroscopy

The fields of view of Extremely Large Telescopes will contain vast numbers of spatial sampling elements (spaxels) as their adaptive optics systems approach the diffraction limit over wide fields. Since this will exceed the detection capabilities of any realistic instrument, the field must be dilutely sampled to extract spectroscopic data from selected regions of interest. The scientific return will be maximized if the sampling pattern provides an adaptable combination of separated independent spaxels and larger contiguous subfields, seamlessly combining integral-field and multiple-object spectroscopy. We illustrate the utility of this diverse-field spectroscopy (DFS) to cosmological studies of galaxy assembly. We show how to implement DFS with an instrument concept: the Celestial Selector. This integrates highly multiplexed monolithic fibre systems and switching networks of the type currently available in the telecommunications industry. It avoids bulky moving parts, whose limitations were noted in Paper I. In Paper III, we will investigate the optimization of such systems by varying the input–output mapping

Strategies for spectroscopy on extremely large telescopes - III. Remapping switched fibre systems

We explore the use of remapping techniques to improve the efficiency of highly multiplexed fibre systems for astronomical spectroscopy. This is particularly important for the implementation of diverse field spectroscopy (DFS) using highly multiplexed monolithic fibre systems (MFS). DFS allows arbitrary distributions of target regions to be addressed to optimize observing efficiency when observing complex, clumpy structures such as protoclusters which will be increasingly accessible to extremely large telescopes. We show how the adoption of various types of remapping between the input and output of an MFS can allow contiguous regions of spatial elements to be selected using only simple switch arrays. Finally, we show how this compares in efficiency with integral-field and multi-object spectroscopy by simulations using artificial and real catalogues of objects. With the adoption of these mapping strategies, DFS outperforms other techniques when addressing a range of realistic target distributions. These techniques are also applicable to biomedical science and were in fact inspired by it

Fibre modal power distributions in astronomy and their application to OH-suppression fibres

Knowledge of the modal power distribution (MPD) in multimode optical fibre is crucial for the design of OH-suppressing fibre systems based on single-mode fibre arrays. MPDs allow us to estimate the minimum number of modes required to provide good data quality for astronomy so that we can reduce the size and cost of the single-mode array. This paper shows how the MPD of multimode fibres changes when fed with the telescope point spread function and when illuminated with an image of the telescope exit pupil via a field lenslet under conditions of ideal, natural and partially corrected seeing. We show that OH-suppressing fibres operating at 800 nm require arrays of single-mode fibres that will be challenging to manufacture. The complete J and H bands, however, require as few as 40–80 modes

The cosmological evolution of the radio source population

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